Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gases

Abstract

Detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are obtained for different air temperatures, air velocities and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors. For the measurement of the local film thickness and film velocity a new optical instrument — based on the light absorption of the liquid — has been developed, which can be used at high temperatures with evaporation. The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase. The results utilizing the two models for the liquid film show that the film exhibits laminar rather then turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface. Using time averaged values for the thickness, the velocity and the roughness of the film the code leads to relatively accurate predictions of the interaction of the liquid film with the gas phase.

Two-dimensional mapping of falling water film thickness with near-infrared attenuation

“…Debrégeas et al (1995) reported the thickening of viscous bursting freely suspended films by measuring the attenuation of a 0.5-mm-diameter infrared beam. Numerous similar measurements can be found elsewhere (Yang et al 2010(Yang et al , 2011Wittig et al 1992;Sattelmayer 1987) where windows were made of glass or quartz. In each case, different wavelengths have been investigated to achieve an adequate absorption coefficient according to the thickness range under investigation.…”

Effects of location, shape and width of a suction slot on the water removal performance of a hollow stator blade

“…The internal passage of the hollow stator blade was connected to a water collector (15) to allow the water sucked from the blade surface to enter the water collector through the pressure difference generated by a vacuum pump (16). The exhaust steam entered a condenser (11), where it was cooled down to water and collected by a water tank.…”

“…Wittig et al 11 reported that the water film surface velocity on a flat surface ranges from 0.5 m/s to 3.5 m/s when the main air flow velocity varies from 30 m/s to 60 m/s. The water film velocity measured by Li et al 10 ranges from 1 m/s to 4 m/s with a main air flow Mach number of 0.3.…”

Effects of Fuel Nozzle Displacement on Pre-Filming Airblast Atomization

“…Sattelmayer and Wittig (1986) showed that in the prefilming airblast atomizer the wavy liquid films influence the velocity of gas phase. Wittig et al (1992) found that the pre-filming flow was almost laminar, and the turbulent air or the waviness of the film didn't induce significant turbulence into the film. Brena de la Rosa (1992) inspected the effect of air swirl on the structure of a liquid spray.…”